Abstract: The heat activated vent for releasing an excess internal pressure in a container which pressure accompanied by an abnormal rise in an internal temperature of the container uses a spring to store sufficient energy to propel a barb or spike to pierce a thin diaphragm. A pierceable thin diaphragm is positioned adjacent to the sharp end of the barb and is arranged to provide a fluid tight seal across an open end of a hollow vent housing. The spring is in the form of a leaf spring having a diaphragm piercing upright barb at one end thereof while the other end of the leaf spring is supported in a fixed position within the housing. The end of the spring carrying the barb is normally retained in a position wherein the barb is spaced from the diaphragm by a preshaped end of a cantilevered beam of a material having a memory capability.